My clients use some portal system and he send newsletter to surcibed users.
Last day he sent 3000 mail

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Ok, that explains these lines

Can you please try to send an email to your own email address on the server and post exactly the lines that where added for this delivery.

Then have a look at /var/spool/mail if the email has been added to a file with the name of you email user. If not, have a look in the maildir of your useraccount and check if there are any messages in one of the sub directorys.